Measurement of Dissolved Oxygen in Swamp Waters. Further Modification of the Winkler Method

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Abstract
1. A modification of the iodine-difference Winkler method is described which involves a preliminary clarification of a single sample, from which two smaller samples are siphoned. 2. This makes possible estimations on extremely muddy and polluted water and avoids an error in the standard iodine-difference method which is very large with highly polluted waters. 3. The iodine is added with the clarifying reagents to the original sample, thus avoiding the necessity for quantitative addition of iodine to two separate samples, which is another potential source of error in the standard method. 4. Estimations on swamp water saturated with air under standard conditions indicate that the method is accurate to within 0.2 mg. O2/l. 5. With polluted water, having an oxidation-reduction potential (Eh) of less than +100 mV., ‘negative’ figures for oxygen content are obtained. The cause of this phenomenon could not be discovered but, since this potential indicates anaerobic conditions, the method is not thereby affected. 6. An improved iodine-titration end-point is described involving the use of a magnetic stirrer. 7. Direct spectrophotometric estimation of iodine is shown to be as accurate as, and very much more rapid than titration, and particularly suited to the iodine-difference method.